In the evening the hedgehog makes its low rounds on the grass, close to the walls, threaded through those narrow passages between the garden and the asphalt. That’s exactly where things get bad. The European hedgehog is going through a bad time: in recent years the species has entered the category Near Threatened of the IUCN, that is, “near threatened”, and among the pressures that return most often are habitat fragmentation, roads and everything that makes the landscape harder to cross. In some local populations, traffic is indicated as a very heavy cause of mortality.
The word extinction travels quickly and immediately makes headlines. The data, for now, tell a very serious and very concrete trajectory: an animal that was common until a few decades ago is disappearing from many European territories, and the decline approaches or exceeds 30% in various areas over the course of ten years. Within this framework a discovery has arrived that has the quality of useful things: small, precise, perhaps decisive.
Oxford University published on Biology Letters a study that, for the first time, shows something that has remained in the shadows until now: hedgehogs can also hear ultrasound. The researchers measured the brainstem response in 20 hedgehogs recovered from Danish wildlife centers, using electrodes and short sound signals, and saw that the species’ hearing covers a range from 4 to 85 kHz, with a maximum sensitivity around 40 kHz. To clarify: we human beings stop much earlier, around 20 kHz.
The study added another piece that makes the discovery more solid. Through micro-CT scans of the ear, the team reconstructed some anatomical structures of the hedgehog in 3D and found characteristics compatible with this perception of high frequencies. Translated out of academic language: the hedgehog, on that side, was already equipped. It was enough to notice it.
From cars to robot lawnmowers
This is where the idea that is causing discussion comes from: editing sonic repellents on cars or other devices, so as to push the hedgehogs to move away before reaching the worst point. Oxford talks openly about a possible collaboration with the automotive industry to design these systems. We are still far from the gadget being ready to sell: for now the biological basis exists, all the decisive part is missing, i.e. understanding whether the hedgehog really reacts in the way hoped for, with what frequency, at what distance and with what side effects on other animals.
The reference to the gardens, however, comes almost naturally. The same researchers also cite the risk of collisions with robot lawnmowers, and the literature on this is already less theoretical: previous studies have shown that some models can injure hedgehogs and that little ones, above all, remain exposed because many machines only detect them after contact. This is why the idea of ultrasound also affects lawn mowers and outdoor tools, as well as cars.
In the meantime, the garden remains the first piece of the road
Meanwhile, the hedgehog’s protection still comes from the most material things. Fragmented habitats, closed fences, treated lawns and overly tidy spaces deprive them of shelter and passages. Projects like Hedgehog Street have insisted for years on a simple and very concrete measure: creating small gaps in the fences, approximately 13 by 13 centimeters, to connect the gardens and restore continuity to their nocturnal movements. It seems like a small detail. For an animal that moves low and always looks for a corridor, it changes quite a lot.
The novelty of Oxford is right here. It doesn’t deliver a magical solution, it delivers a serious possibility. In a time in which the hedgehog ends up crushed on the streets or injured in the gardens by cars designed to go straight, the idea of a signal that we do not hear and that it does has something very simple and very intelligent. The hedgehog will continue to come out at sunset. The difference, if anything, lies in those few steps before the asphalt.
